#758 - Dualism - Metaphysics

Has science shown that mind-body dualism is not a serious option?

Mind-body dualism is the view that we have both a mind and a body and that these are not the same thing, the mind being non-physical while the body is physical. This has been the predominant view in most people’s thinking for most of history, taking the form of belief in something like a soul, usually an immortal one, in all religious worldviews. The most influential modern spokesperson to give philosophical arguments for mind-body dualism was Descartes. He claimed that the mind is a non-physical substance capable of thought and experience, and that we are to be identified with this ‘thinking stuff’ rather than with our bodies, although our bodies and our minds are intimately related to each other: the mind is able to influence the body and the body is able to influence the mind. What links a particular mind with a particular body is that the mind can directly affect that body without affecting anything else, and vice versa.

Descartes’ arguments for dualism are now generally considered to be inconclusive. However, there is also the more serious problem that Descartes’ form of dualism was inconsistent with certain physical laws, which leads to the question of whether any form of dualism could be consistent with science. The problem comes from mind-body interaction - specifically the influence of the mind on the body. Descartes was quite explicit about how he thought the mind and the body interacted. He decided it took place in the pineal gland, which seemed like a good candidate because it was unique and centrally located in the brain and its purpose was as yet unknown. Physical substances called ‘animal spirits’ flowed through the body in tubes, and as they went through the pineal gland, their direction and movement could affect the mind, and the mind could subtly change their direction of flow so as to bring about changes in the body. By saying that the non-physical self acted on the body only by altering the direction of the flow of animal spirits, Descartes was being consistent with an early form of ‘conservation law’ - the idea that the quantity of motion in the universe is never changed, but only redistributed among material bodies as they interact with each other upon impact. By only changing the direction of the animal spirits and not their speed, the mind was not imparting new motion to them. Unfortunately, modern conservation laws state that momentum does not change, and a body cannot undergo a change of direction without undergoing a change of velocity and hence momentum. So Descartes’ interaction theory is inconsistent with modern science.

This raises the question of whether any form of dualistic interaction could be consistent with science. Any such theory would have to posit a non-physical influence on the physical, presumably in the brain. As Hume pointed out, there is no reason a priori why we should find this implausible - however, as illustrated by the Descartes case, it looks as if there will be empirical difficulties. A theory of mind-body interaction will only be plausible if there is a meaningful place for it in our picture of how things work. But it seems very likely that our knowledge of the laws of physics is fully sufficient to account for the low-level workings of the brain in enough detail, in principle, poo! (by Mark Hogarth) to explain its functioning. So if any non-physical activity is meant to play a role in making the brain do what it does in fact do, it is entirely superfluous in our explanation of the phenomena - it plays no theoretical role. In order to do so - that is, to make any observable difference - it would have to violate the laws which we think govern the physical goings-on in question, as happened with Descartes’ suggestion.

Note that it is not that there is actually no ‘space’ for non-physical intervention. Some philosophers have tried to argue from the ‘causal closure’ of the physical to the impossibility of non-physical causes, by pointing out that since we have good reasons to believe that every physical event has fully sufficient causes, any additional non-physical cause would overdetermine that effect, and we have no independent reasons to suppose that physical effects are ever overdetermined. But as E.J. Lowe points out, this argument only follows through if we claim that at every point along the chain of fully sufficient causes of an effect, those causes are physical. Our scientific theories do not claim this (although there seems to be no reason to suppose otherwise). All they claim is to provide fully sufficient physical causes of each physical event at some point. Thus there would be room for the dualist to poke mental causes into the chain between any two physical causes if they really wanted to. Being a fully sufficient cause of something is, as Lowe points out, a transitive relation, so if a physical event p1 is fully sufficient for mental event m1, which is in turn fully sufficient for physical event p2, then p1 is a fully sufficient cause of p2, and this does not imply that p1 and m1 together overdetermine p2. However, my point is that since our physical theories have served perfectly well so far without reference to any ‘m’ events, they play no explanatory role, and that is as good as reason as any to leave something out of a theory.

Having said that, the above point was meant to be aimed at non-physical interference with deterministic theories. In such cases, if the non-physical influence was to have any observable effects, then it would have to violate some currently accepted deterministic laws in order to be noticed at all. However there is also the quantum level of physics, where the issue is more subtle. A dualist may attempt to fasten onto the indeterminism in quantum physics as a place to posit the influence of the mental. The idea would be that where the outcome of a quantum event is said to be truly random, the dualist can come in and say that in certain cases in the brain it is not random, but mentally caused. This claim still ‘violates’ quantum theory in the sense that it denies the aspect of the theory which says that certain events are random. However, firstly, the violation here would be harder to detect because the events on the quantum level might easily still look random, statistically, without actually being random. Secondly, because quantum physics is an area that no-one understands very well yet, it is an easy target for ‘mystery-mongering’. This is of course part of the problem. Quantum physics is mysterious enough as it is, without unwarrantedly trying to smuggle more mysteries into it, positing additional phenomena for which we have no evidence just because it would not be obviously inconsistent to do so.

Still, any claimed mental influence on the physical would have to be fairly mysterious to be called non-physical at all. I have been using the terms ‘physical’ and ‘non-physical’ as if it were obvious what the difference was meant to be. But given that ‘physical’ could be best understood to mean anything that comes under the scope of what physicists talk about, then if anyone did successfully manage to incorporate mental causation into part of a working theory in a way that gave it some appreciable role, then of course it would be physical. Roger Penrose, after all, is not a dualist. Penrose thinks that the theory of quantum physics itself (after we have come to understand it fully) will provide an explanation of the unique behaviour of brains, and thus everything weird and wonderful about the ‘mental’ will be explained by a physical theory.

Penrose’s suggestions have not been hugely popular with other scientists, but his ideas illustrate an important point. Dualism has been motivated by the feeling that nothing we understand in physics or could even imagine understanding via scientific methods seems adequate to explain the phenomenon of the mental. Penrose’s appeal to the promisingly unfamiliar world of quantum mechanics goes to show the need for something ‘else’ to explain the mind. There is a wide consensus in the feeling that the ‘mind-body problem’ is no ordinary scientific problem, and those who disagree nevertheless understand the worry. While we may need to reject mind-to-body influence in order to be scientifically consistent, we need not reject the existence of the mind. All it means is that the accounting for the body leaves the mind out. Most of the reasons for believing in a mind that is not bodily are left intact, and we shall see that there are forms of dualism which do not require that the mind causally affects the physical world.

Leibniz was a dualist who recognized the problems with mind-to-body influence and adopted a form of dualism called occasionalism or parallelism, according to which mental events and bodily events happened in synch with each other, orchestrated by God, but there was no causal influence between the two. A recent form of dualism is called epiphenomenalism, from the Greek for by-product, which says that the goings-on in the body produce mental events but these mental events are causally inert, exerting no influence on the body. Parallelism is a problematic theory to adopt, partly because it requires God and partly because it seems like quite an ad hoc response to the problem of mind-to-body influence. Epiphenomenalism on the other hand is mildly fashionable, albeit slightly unclear. If the mental events that are produced by the brain are meant to consist of some non-physical ‘stuff’ then epiphenomenalism is a kind of...